Baseball Therapy: The Fly Ball … Revolution?

The fly-ball revolution (aka, the air-ball revolution, aka the launch-angle revolution, aka the “Josh Donaldson said what?” revolution) is here. Sorta. While fly-ball rates are up overall in the past few years, they are not at historically high levels.

And to quote my former boss here at BP:

Home runs per fly ball are up, meaning that when hitters do hit a fly ball, they are getting more out of them. That distinction matters. If hitters have been doing something successful in the past few years, it’s probably not the launch angle, it’s that they’ve found a way to hit the ball harder. Maybe it’s just that players lately are bigger than they used to be.

After all of the stories about the early-season success stories, and players who were lifting the ball more and lifting their stats as a result, there’s been a few moments of quiet reflection. Rob Arthur of FiveThirtyEight showed that the revolution has essentially hurt as many batters as it has helped. ESPN’s Buster Olney talked to team executives who were much more sanguine about the revolution.

Sure, some guys have raw power, were wasting that power by not hitting fly balls, and have adjusted their swings upward to take advantage of that natural ability. Not everyone has the power to hit the ball out of the park, and if you don’t hit it out of the park, BABIP on fly balls is around .150. That’s a recipe for hitting like a pitcher.

This is being called the fly-ball revolution, as if this was something new, but players have always messed around with their swings. Sometimes it has even worked. Just because we have a fancy new toy (StatCast) that can put fancy new numbers (launch angle) on the issue, it doesn’t mean that we haven’t seen this movie before.

Warning! Gory Mathematical Details Ahead!

I used Retrosheet data from 2003-2016. Going back that far, we do not have launch-angle data, but we do have data on the types of batted balls that were struck (i.e., fly ball, ground ball, pop-up, line drive). Even if these are not always the most reliable data, they do give us some idea of whether a player was getting a little more loft on the ball, and we can see how he was doing from year to year.

For these analyses, I also added in a small wrinkle. Previous research has shown that when it comes to batted-ball types, fly ball is the opposite of ground ball (i.e., there are fly-ball hitters and ground-ball hitters—no surprise there) but that line drives are a) their own species, and b) largely unreliable. There is some skill in hitting line drives, but it is hard to repeat, and how many line drives you hit seems to be unrelated to where you fall on the ground-ball/fly-ball spectrum.

So, for these analyses, I looked only at balls that Retrosheet coded as fly balls/pop-ups or ground balls. This will give us a truer look at which approach a player was taking during those years. First, it’s worth noting that there were about 250 cases in those 14 years where a batter increased his fly-ball rate (and had 250 plate appearances in each season to prove it) by more than five percentage points.

I’d like to say that I did some crazy numerical gymnastics on this one. (And I did, but frankly, I came up with the same story each time.) So, I’m going to present the simplest form of what I did. I took all year-to-year pairs with the same batter, again minimum 250 PA in each season. I took a simple difference from year to year in his “fly-ball percentage” and looked at how well that correlated with changes in his performance for several other outcomes that we care about.

For example, in the case of strikeout rate, I’m looking at the correlation between the change in fly-ball rate from Season 1 to Season 2 and the change in strikeout rate from Season 1 to Season 2. All stats are per plate appearance, unless noted.

Pardon me while I yawn.

(I re-ran these with only players who showed an increase in their fly-ball rate, and then only among those who had one of those five-point jumps. Same findings.)

Correlation tells us the strength of the relationship, not its magnitude, although when I looked into that, hitting more fly balls did pretty much what we might imagine. Hitters—on average—gained a few home runs and lost a few more singles for each percentage point of fly-ball rate that they added, although the home runs are worth more. Saying “there’s no slug on the ground” is nice, but there is OBP on the ground and there might not be anything more than fly outs waiting in the air.

The correlations are the real story here, though. They are very weak. A hitter probably can sell out for lift and hit a few more homers, but weak correlations mean that this is not a guarantee. And not only may your mileage vary, but your mileage will vary a lot. Hitting more fly balls is not a magic solution to becoming a better hitter. It might work. It might not.

If fly balls haven’t notably increased and even when they have, the evidence points to that not being a panacea, what is going on in MLB?

Anyone who’s taken a physics class knows that the result of a batted ball is going to depend on both the launch angle and the exit velocity, acting in tandem. A fly ball hit with a modest exit velocity isn’t going to carry anywhere but the left fielder’s glove. If you hit the ball 100 mph, but hit it on the ground, it might scoot through for a single, but it might also just end up being a 4-3 ground out. We know this instinctively. “Hit the ball really hard and somewhat upward” is true, but hardly revolutionary.

Much like launch angle, we don’t have exit-velocity stats going back before 2015. The closest thing that we have (subjective ratings of whether a ball was “hard hit”—not the best methodology, but sometimes flawed data is better than no data—back to 2002) do show an increase over time in general and on fly balls specifically. And we know again that players have gotten bigger during that time period as well.

It’s reasonable to think that players might have a little more oomph behind their swings now than they did 15 years ago. If you swing really hard, you’ll run into a few fly balls, and a few more of them will leave the yard than before. Is it possible that we have, not so much a fly-ball revolution, but a “hitting the ball really hard” revolution? Would that even be a revolution? It certainly wouldn’t be a revelation.

Won’t Get Fooled Again

Quick, name five bands/musical acts. The first five that pop into your head. Doesn’t matter who. Go.

1.
2.
3.
4.
5.

Obviously, I’m not there inside your head (or … am I?) to know what you picked, but I’m guessing that all five have the common thread that they have received national radio airplay. I didn’t ask you to name five famous bands. Just five bands. And yet you probably picked five that most people would recognize as a band that charted on the Billboard 100 at some point. (And I promise I won’t tell anyone about no. 3 being the Backstreet Boys.)

The vast majority of bands out there are random local acts of whom no one has ever heard and are mostly just people who like to jam in someone’s garage. They play a few shows here or there at the tavern out on Main St. (It makes them happy, so, why not?) It’s possible that you’ve even seen a few of them, but when pressed you didn’t think of them. Despite the fact that statistically, the vast majority of bands out there are these local acts, you thought of the wildly successful bands.

I’m wondering if the same dynamic isn’t at play with all of this talk of the “fly-ball revolution.” There’s probably some room for a few players who had untold, untapped power unlocked by focusing on fly balls. They met with success, so they kept going with it. Their success made for a good story to write about, and so their cases got famous. The advent of the new Statcast metrics tied in nicely, and provided some nice color to those articles and a vocabulary to talk about what had happened.

But was it a revolution or a couple of convenient cases that fit a pleasing narrative? What about the guys who have tried the fly-ball thing and gotten awful results? What about the guys who may have messed around with a fly-ball swing in batting practice, realized it wasn’t going to work for them, and then went back to what got them into the majors to begin with?

Perhaps I’m not being fair to Statcast. One could make the case that the true superpower of Statcast is in teaching players to optimize their launch angle to within a few degrees on the compass, rather than the more crude “hit fly balls,” although I have to wonder how realistic it is to fine tune a launch angle when we’re talking about using a big stick (with the kind of force it would take to make a good launch angle worth anything) to hit a small ball traveling at 90 mph and bending at weird angles from 60 feet away.

I kind of wonder if the “fly-ball revolution” is actually all in our heads, a figment of our imagination borne one part of availability bias, one part of Statcast making it salient (and in fairness, perhaps legitimately providing the data for a couple of those hitters to change their approach), and one part needing to explain the home run spike with something more than “hitters are bigger now and are sitting on the fastball and swinging hard.” That’s gonna produce some home runs.

Fly balls themselves aren’t really up. The evidence says that even when hitters do try to hit the ball in the air, it’s a mixed bag as to what it actually accomplishes. What’s really up is home runs, and that seems to have a different explanation. I’d humbly submit that the fly-ball revolution is at the very least overblown in how much of an impact it’s actually making on the game. Maybe there is a revolution going on here, but I think it needs a better name.